I used 5w30 Castrol Edge I think but do a search as there have been lots of threads on this question I'm sure.
Just filled it up today! Bought it from R33SY about 2-3 months ago now, just checked the oil, bone dry! literally, im suprised my engine hasn't seized up! SHIIIIIT!!!
Anywhooooo Castrol Edge 5W30 is what i put in it!
i would say its down to driving style tbh.
i dont do many miles, but when i do i like to have fun, and im hard on the car...i can go from full to min marker in a tank of fuel but i have also done plymouth - london and back and it dropped about 1mm with casual motorway driving.
done it again, having more fun and took about 3/4 of it!